Along with an improvement in integration of LSIs, circuit line widths of semiconductor devices have become finer. As an example of a method for forming exposure masks (exposure masks used in steppers and scanners are also called reticles) that are used for forming circuit patterns in such semiconductor devices, an electron-beam writing technology having high resolution has been used.
For example, there are writing apparatuses that use multiple beams. The use of multiple beams can greatly improve the throughput because it enables irradiation with more beams at a time (in a single shot) than in the case where writing is performed using a single electron beam. In such multi-beam writing apparatuses, for example, multiple beams are formed by letting an electron beam emitted from an electron gun pass through an aperture member having a plurality of apertures. Blanking control is performed on each of the beams. Unblocked beams are each reduced by an optical system, and a substrate placed on a movable stage is irradiated with the resulting beams.
Multi-beam writing uses many beams, resulting in an enormous amount of data for individually controlling irradiation time periods of the beams. To solve such a problem, a considered approach involves causing a plurality of computers to perform parallel processing such that the amount of data processed by each computer is reduced.
One of known multi-beam writing techniques is multi-pass writing that involves dividing a necessary dose into multiple writing (exposure) steps in order to average variations in beam current or reduce the effect of resist heating. In multi-pass writing, for example, writing is repeated while irradiation positions are shifted on a stripe-by-stripe basis.
In multi-pass writing while shifting the irradiation positions, computers configured to perform parallel processing process different data items for each pass of the multi-pass writing. Each computer therefore has to include a large-capacity memory to hold data to be processed. Furthermore, the amount of data transmitted and received by each computer is large. Disadvantageously, it takes a long time to transfer data.